1. Technical Field
The present invention is an improved boss for reinforcing the structural interface between a filament wound outer shell and a non-metallic internal liner in a rounded high pressure vessel.
2. Background Art
In many circumstances, the qualities of lightweight construction and high resistance to fragmentation and corrosion damage are highly desirable characteristics for a pressure vessel. These design criteria have been met for many years by the development of high pressure composite containers fabricated of laminated layers of wound fiberglass filaments or various types of synthetic filaments which are bonded together by a thermal-setting epoxy resin. An elastomeric or other non-metal resilient liner or bladder is suspended within the filament wound shell to seal the vessel and prevent internal fluids from contacting the composite material.
Filament wound vessels often are constructed in a spherical shape or a cylindrical shape with generally spherical ends for use in high pressure applications. A boss is used to reliably join the internal liner with the outer composite shell at pressurization ports in the outer shell such that fluid is prevented from penetrating between the liner and the shell. In many applications, such as in the aerospace industry, composite pressure vessels are required to contain extremely high pressures, operating at 25,000 p.s.i. with design burst values in the range of 50,000 p.s.i. Consequently, as internal pressure increases, the interface of the boss, the liner and the outer shell is subjected to extreme structural loading.
More particularly, as pressure within the vessel is increased, bearing stress is generated between the boss and the composite shell, resulting in a steep strain gradient through the shell, with the inner strains being much higher than those at the outer surface. Shearing stress develops between the boss and the internal liner due to relative displacement discontinuities resulting from nonuniform loading during internal pressurization. In addition, radially extending support members on the boss are subjected to unacceptable levels of bending stress which can result in fracture of the boss.
Moreover, it is critical that during the pressurization of the vessel the liner and outer shell remain firmly engaged with the boss, despite the adverse loading to which the liner and shell are subjected. The present invention is directed toward overcoming the above mentioned loading and sealing problems by providing a unique construction in a boss for a filament wound pressure vessel of the character described.